The human T-cell leukemia virus type I (HTLV-I) is a retrovirus that is the causative agent of a variety of clinical disorders, including an aggressive and fatal T-cell leukemia. Malignant transformation associated with HTLV-I infection is strongly linked to the synthesis of the: vitally-encoded transcription factor Tax. The Tax protein is critical to the life cycle of the virus, as it plays a major role in the transition from viral latency to high-level virion production. Tax mediates this transition via strong activation of HTLV-I transcription, which leads to efficient replication of the virus. Viral gene expression is stimulated following the formation of a stable promoter-bound complex containing Tax, the cellular transcription factorCREB and the cellular coactivators CBP/p300. Much of our current understanding of Tax,activated HTLV-! transcription has come from in vitro binding and transient transfection assays, neither :of which directly assess physiological relevance of the interactions under study. In this application, we propose to explore the transcriptional regulation of the natural, chromosomaily-integrated proviruses in HTLV-I infected T-cells. These studies will investigate the dynamic interaction between Tax, cellular transcription factors, coactivators and corepressors at the HTLV-I promoter in living cells. We will also characterize the kinetics of transcription complex assembly, transcriptional activation and RNA synthesis, following Tax induction in human T-cells. Similar studies will also be carried out on chromatin templates in vitro. These experimental approaches are designed to mimic to further our understanding of transcriptional regulation of HTLV-I. We also propose to characterize the effects of rationally designed polyamides on HTLV-I transcription and Tax function both in vivo and in vitro. We have a comprehensive set of polyamides that should enable inhibition of Tax binding specifically at each viral CRE. This will allow dissection of the role of each viral CRE in Tax-transactivation. The long-term goal of this study will be the synthesis and characterization of specific, high affinity polyamides that will block Tax function in the cell. Together these studies provide a diverse, integrated approach to the study of Tax function, both in vitro and in vivo. Our studies should yield a greater understanding of the multiple mechanisms of Tax transcriptional activation in the HTLV-I-infected T-cell.